/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jasper.el;

import javax.el.*;
import javax.servlet.jsp.el.ImplicitObjectELResolver;
import javax.servlet.jsp.el.ScopedAttributeELResolver;
import java.util.List;

/**
 * Jasper-specific CompositeELResolver that optimizes certain functions to avoid
 * unnecessary resolver calls.
 */
public class JasperELResolver extends CompositeELResolver {

	private final int appResolversSize;
	private int size;
	private ELResolver[] resolvers;

	public JasperELResolver(List<ELResolver> appResolvers) {
		appResolversSize = appResolvers.size();
		resolvers = new ELResolver[appResolversSize + 7];
		size = 0;

		add(new ImplicitObjectELResolver());
		for (ELResolver appResolver : appResolvers) {
			add(appResolver);
		}
		add(new MapELResolver());
		add(new ResourceBundleELResolver());
		add(new ListELResolver());
		add(new ArrayELResolver());
		add(new BeanELResolver());
		add(new ScopedAttributeELResolver());
	}

	/**
	 * Copied from {@link org.apache.el.lang.ELSupport#coerceToString(Object)}.
	 */
	private static final String coerceToString(final Object obj) {
		if (obj == null) {
			return "";
		} else if (obj instanceof String) {
			return (String) obj;
		} else if (obj instanceof Enum<?>) {
			return ((Enum<?>) obj).name();
		} else {
			return obj.toString();
		}
	}

	@Override
	public synchronized void add(ELResolver elResolver) {
		super.add(elResolver);

		if (resolvers.length > size) {
			resolvers[size] = elResolver;
		} else {
			ELResolver[] nr = new ELResolver[size + 1];
			System.arraycopy(resolvers, 0, nr, 0, size);
			nr[size] = elResolver;

			resolvers = nr;
		}
		size++;
	}

	@Override
	public Object getValue(ELContext context, Object base, Object property)
			throws NullPointerException, PropertyNotFoundException, ELException {
		context.setPropertyResolved(false);

		int start;
		Object result = null;

		if (base == null) {
			// call implicit and app resolvers
			int index = 1 /* implicit */ + appResolversSize;
			for (int i = 0; i < index; i++) {
				result = resolvers[i].getValue(context, base, property);
				if (context.isPropertyResolved()) {
					return result;
				}
			}
			// skip collection-based resolvers (map, resource, list, array, and
			// bean)
			start = index + 5;
		} else {
			// skip implicit resolver only
			start = 1;
		}

		for (int i = start; i < size; i++) {
			result = resolvers[i].getValue(context, base, property);
			if (context.isPropertyResolved()) {
				return result;
			}
		}

		return null;
	}

	@Override
	public Object invoke(ELContext context, Object base, Object method,
	                     Class<?>[] paramTypes, Object[] params) {
		String targetMethod = coerceToString(method);
		if (targetMethod.length() == 0) {
			throw new ELException(new NoSuchMethodException());
		}

		context.setPropertyResolved(false);

		Object result = null;

		// skip implicit and call app resolvers
		int index = 1 /* implicit */ + appResolversSize;
		for (int i = 1; i < index; i++) {
			result = resolvers[i].invoke(
					context, base, targetMethod, paramTypes, params);
			if (context.isPropertyResolved()) {
				return result;
			}
		}

		// skip map, resource, list, and array resolvers
		index += 4;
		// call bean and the rest of resolvers
		for (int i = index; i < size; i++) {
			result = resolvers[i].invoke(
					context, base, targetMethod, paramTypes, params);
			if (context.isPropertyResolved()) {
				return result;
			}
		}

		return null;
	}
}